Field
The present invention relates to an apparatus for artificially weathering or testing the lightfastness of samples and to a method for artificially weathering or testing the lightfastness of samples.
Description of Related Art
In apparatuses for artificial weathering, an assessment of the weathering-induced aging response of a sample, in particular a flat material sample, is performed, wherein the sample is subjected to artificial weathering. For this purpose, such apparatuses generally have a weathering chamber, in which holding means for holding samples to be weathered and a radiation source for applying radiation, in particular UV radiation, to the samples are arranged.
In such apparatuses for artificially weathering or testing the lightfastness of material samples, the intention is usually to estimate the life of materials which are continuously subjected to natural weather conditions during use and are therefore impaired under climatic influences such as sunlight, solar heat, moisture or the like. In order to obtain good simulation of the natural weathering conditions, it is advantageous if the spectral energy distribution of the light generated in the apparatus at least corresponds to that of the natural solar radiation, for which reason xenon gas discharge lamps are used as radiation source in such devices. In addition, accelerated aging testing of the materials is achieved substantially by virtue of very intensified radiation, in comparison with natural conditions, of the samples, as a result of which the aging of the samples is accelerated. Therefore, after a comparatively short period of time, it is possible to draw a conclusion on the long-term aging response of a material sample.
A large proportion of the material samples investigated in artificial weathering devices consists of polymeric materials. In the case of such materials, the weathering-induced impairment is substantially caused by the UV component of solar radiation. The photochemical primary processes occurring in the process, i.e. the absorption of photons and the generation of excited states or free radicals, are independent of temperature. Conversely, the subsequent reaction steps with the polymers or additives can be temperature-dependent, with the result that the observed aging of the materials is likewise temperature-dependent.
In the previously known weathering test devices, usually a xenon gas discharge lamp is used as radiation source. Such a xenon gas discharge lamp can be used, as is known, to simulate the solar spectrum quite well, but a conventional xenon lamp only has a nominal life of approximately 1500 hours at maximum irradiance. This means that the lamp can be operated at the maximum irradiance for this time period.
Furthermore, in principle metal halide lamps or fluorescent lamps can also be used as radiation sources for weathering devices. These lamps generally have a longer life than xenon lamps, but tend to be inferior to xenon lamps in terms of their spectral quality.